Research On The Amplified Hydrological Effect And Distributed Model Of Urban Stormwater

Fast-developing urbanization caused serious impact on hydrologic circle law, leading to temporal and spatial change of hydrologic circle factors. In recent years, urban flood disasters have happened more and more frequently, and occurred in more and more cities in China. Urban flood disasters have become one of severe water problems faced by cities in China. It is particularly urgent to understand and analyze the amplification effects of urbanization on urban flood. A distributed model of urban stormwater is an effective means to study urban hydrologic circle and the amplification effects of flood. However, complex underlying surfaces and inadequate urban storm water data restrict the establishment of distributed model of urban storm water. As satellite remote sensing (RS) data, radar data and geographical information system (GIS) are increasingly applied to basin hydrological models, it is of scientific significance and actual application value to establish a distributed model of urban stormwater based on RS and GIS for studying hydrological process simulation and amplification effects of urban flood.Regarding Wuhan as studying area, this thesis analyzes the evolvement rule of amplification effect driving factors of urban flood using spectral analysis technique and extraction methods of impervious area, then establishes a distributed urban stormwater model using RS data and GIS analysis technique, and verifies and applies the model in Shilipu catchment area. Combining this model with compared experiments in runoff experimental field, this thesis reveals the amplification effects of urbanization on urban flood in three aspects of rainfall, runoff producing and water converging to provide technical support for urban flood emergency management, pipe-network drainage ability design and land-use planning. The main contents are as followed:(1)Extracting an amplification effect driving factor from rainfall, runoff producing and water converging respectively, that is rainfall intensity, percentage of impervious area and the density of drainage pipeline, this thesis uses a number of statistic-testing methods to analyze how the driving factors are changing in space and time. It turns out that, since 1960 the number of heavy rain or rainstorm day and continuous rainfall greater than 100mm and 150mm has been obviously increasing, and regarding to Short-term Adjacent Rainfall Intensity Grading, the annual rainfall amounts and total duration of heavy rain (whose one-hour rainfall is between 8 and 20mm) and rainstorm (whose one-hour rainfall is greater 20mm) also have increase trends. Otherwise, impervious area since 1990s has been expanding centered on Yangtze River with opposite sharply reduced lake surface area. And the length of pipeline in Wuhan city is also growing year by year while there is a boom in 2007 with a 238.5% jump. As a result, the current length is about seven times of 1990's.(2)This thesis establishes a friendly RS-and-GIS-based distributed stormwater model, whose input formats straightly support several GIS layers and vector data, including high-precision DEM layers, land-use classification layers, normalization vegetation index layers, building height layers and underground pipeline layers; as well as hydrological information layers of spatial distribution layers of time-sequenced rainfall, daily temperature and initial soil water content. Of these layers, all except underground pipeline layers are acquired from multi-source satellite remote sensing images and radar data by means of RS and GIS analysis techniques. Through judging the land-use types of grid, runoff process chooses interception, evapotranspiration, infiltration and surface impoundment for various hydrological combination. On the other hand, Water converging forms include nonlinear-reservoir converging for buildings, two-dimension hydrodynamic slope converging for surface flow and one-dimension hydrodynamic converging for underground pipelines, coupling these three forms through inspection wells into "roof-surface-pipelines" converging system.(3)Taking Shilipu catchment area in Hanyang as computational area, this thesis acquires the layers for model input by remote sensing data processing then calibrates and validates the established distributed stormwater model. The simulation results show that the established model performances well in Shilipu catchment area with the average Nash-Sutcliffe efficiency coefficient of 0.78 and 0.67 in calibration and validation periods. Furthermore, the result of situational application on storm waterlogging in Shilipu catchment area shows that, when the rainfall exceeds 5-year-frequency precipitation, surface water will pond around Bailing Road intersection and Jinlong Garden in Baihe Street while exceeds 20-year-frequency precipitation the ponding area reaches about 13950 m2, and maximum depth 18cm.(4)Conducting artificial rainfall experiments in runoff experimental field in Wuhan University, then building mathematical model and designing some scenes into experimental field, this thesis gets the response of magnification of flood runoff coefficient and flood peak to rainfall intensity, percentage of impervious area and density of drainage pipeline. The result shows that when rainfall intensity is constant, percentage of impervious area and density of drainage pipeline show parabolic and linear growth potential respectively as magnification of flood runoff coefficient and flood peak increase while rainfall intensity shows powerful negative correlation. According to these correlations, response functions of magnification of flood runoff coefficient and flood peak to three driving factors are established with reasonable simulations that R2 equal to 0.76 and 0.83. Next applying the established function to Shilipu catchment area, comparing to 440 situational simulations of mathematical model, it turns out that flood runoff coefficient magnification and flood peak magnification of above methods are similar, and almost show the same changing.(5)Spreading the response functions in use to major area of Wuhan city, the result shows that magnification of urban stormwater runoff coefficient and flood peak are rising year by year as impervious area and density of drainage pipeline constantly increase in Wuhan. For instance, under the existing drainage pipe network design standards, that is one-year-frequency precipitation, flood runoff coefficient in 2011 amplifies 1.36 times compared to the value in 1991, while 1.83 times of flood peak value.